The present invention relates generally to water purification and more particularly to water purification using organic additives that include organic salts and salts of organic polymers.
A reliable supply of fresh water is necessary for human consumption, for energy conversion technologies, for irrigation, and for other important uses. Many populated areas are in short supply of fresh water and must rely on water purification technologies such as desalination to provide for, or at least add to, their supply of fresh water. Middle Eastern countries, the Canary Islands, and Mauritius, for example, rely on desalination plants to produce fresh water from seawater. Seawater is a complex substance having a high concentration of sodium chloride and a wide variety of other impurities. Desalination removes most of the sodium chloride and other impurities to produce purified water.
A variety of desalination methods have been reported. They include gas-hydrate formation methods and high-pressure, reverse osmosis methods. Gas hydrate formation methods were examined during an intense period of desalination research from about 1960-1980. A gas hydrate formation method might involve pumping an additive gas though a long tube hundreds of feet below the surface of the sea. Under these conditions of high pressure and low temperature, molecules of additive gas combine with water molecules from the seawater to form a solid, crystalline clathrate known as a xe2x80x9cgas hydratexe2x80x9d. The crystalline gas hydrate includes gas molecules trapped inside cages of tightly bound water molecules. The crystalline gas hydrate is physically separated from the seawater and/or brine (the brine includes the impurities removed from the seawater) and washed to remove any impurities coated on the gas hydrate crystals. The washed crystals are then degassed to produce fresh water. The additive gas may be recovered, recompressed, and recycled if desired.
Current reverse-osmosis desalination methods require high pressures and employ membranes that filter away many of the impurities from xe2x80x9cfeed waterxe2x80x9d (i.e. water with undesired impurities to be removed) and reduce the salt levels to 300 ppm in a single pass. While these membranes are very effective, they are also subject to fouling and scaling from impurities in the feed water. Efforts to eliminate fouling by pretreating the feed water with chlorine to kill bacteria and algae, and to eliminate scaling by adjusting the pH of the feed water to minimize precipitation of insoluble calcium salts and silica, have been met with limited success. Membrane fouling and scaling remains a constant problem. Moreover, reverse osmosis processes are very expensive due to high-pressure requirements, typically 70-80 bar.
In 1996, the Desalination and Water Purification Research and Development Program was authorized by Congress. Information relating to this program can be found at the following website: www.usbr.gov/water/content/c_desal.html. The primary goal of the Program is the development of a xe2x80x9ccost-effective, technologically efficient, and implementablexe2x80x9d means to desalinate water. This program has provided support for the development of new membranes, the application of gas hydrate-assisted desalination, and the design of pumps and vessels, and pilot plant scale testing. While pilot plant scale testing indicated that the energy cost for the production of one cubic meter of fresh water from seawater could be reduced, it remains unlikely that current desalination technology is economically viable in competitive markets. Thus, there remains a need for more efficient water purification methods such as desalination.
Therefore, an object of the present invention is to provide an efficient water purification method.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention includes a water purification method. The method includes contacting feed water with at least one organic salt at a temperature sufficiently low to form brine and organic salt hydrate crystals. The organic salt hydrate crystals are separated from the brine, rinsed with fresh water, and melted to form a solution comprising water and at least one organic salt. Fresh water is then separated from the solution.